1. Field of the Invention
This present invention relates to novel bacterial barrier devices. More specifically this invention relates to improved and clinically acceptable intraluminal catheters and vascular surgical shunts. The present invention discloses a bacterial barrier device which placed circumferentially around an intraluminal catheter (or surgical shunt) and positioned as just within the urethral orifice releases oligodynamic silver ions in a narrow circumferential band thus serving as a barrier to entry of bacterial infection and reducing the incidence of nosocomial problems.
2. Description of the Prior Art
Silver has long been known as an oligodynamic metal. Goodman and Gilson (1943) attributed the antibacterial properties of silver to silver ions which precipitate the protein of bacterial protoplasm. The precipitated protein continues to slowly liberate small amounts of silver ions thus sustaining an antiseptic action. Silver nitrate is routinely instilled in infants' eyes for the prophylaxis of ophthalmia neonatorum. Sollmann (1943) described the action of silver nitrate as occuring in two stages, first, an immediate germicidal effect by the direct application of silver ions and later an antiseptic effect produced by re-ionization of silver protein compounds.
Fromberg and Heiss (1937) using agar plates infected with M. pyogenes var. aureus, confirmed the inactivity of clean, pure silver wire but demonstrated that such a wire could be activated by coating one end with silver chloride producing a zone of inhibition. I. B. Romans, Antiseptics, Disinfectants, Fungicides and Chemical and Physical Sterilization, "Silver Compounds", 2nd Ed., G. Reddish editor, Philadelphia, Lea & Febiger (1957).
U.S. Pat. No. 2,121,875 Kruse (1938) describes a process for anodically coating surgical instruments and silver plates with oligodynamic silver chloride by passing current through such article while immersed in a dilute sodium chloride solution. Articles coated according to Kruse's process needed to be periodically reactivated or recoated.
Ellis in U.S. Pat. No. 4,027,393 (1977) reported that laboratory tests with Pseudononas Aeruginosa, Proteris vulgaris, Staphyloccus aureus and Escherichia coli, bacteria normally found in wounds, have verified that silver electrodes have a bacterial effect at currents of one tenth the magnitude necessary when other electrode elements are used. Ellis while principally directed to dental sterilization recognized the long standing problem of bacterial infection with catheters. Ellis proposed the sterilization of indwelling catheters using silver particles dispersed in the elastomeric catheter wall. The negative electrode is attached to the patient's body or in the effluent. Ellis also proposed to make the silver anode an intraluminal electrode with the silver anode designed as a bladder insert attached to the tip of a wire lead which extended ahead of the catheter.
Neither of the Ellis catheters gained clinical acceptance. Both the intraluminal electrode catheter and the catheter with particles of silver dispersed throughout the length of the elastomeric catheter suffer from serious clinical deficiencies. In the case of the catheter with silver particles dispersed in the elastomeric catheter, only those silver particles lying in the outer surface would release silver ions from the catheter/urethral wall interface; however, the portion of the catheter that contains silver particles must be heavily loaded to insure electrical continuity. This is not only wasteful of silver but also the elastomeric properties of the catheter in the loaded region are significantly reduced resulting in loss of flexibility with attendant difficult and added painful insertion, and continued patient discomfort while indwelling.
More seriously, in the case of the silver particle embedded catheter, the silver containing region extends well into the urethra and is contact with a large extent of mucosal lining and glands. Current flow has the physiological effect on the urethral mucosa and its many mucous secreting glands of enhancing stimulation of fluid flow. In the supine patient, the gradient of excess fluid flow would be toward the bladder rather than to the exterior, tending to wash silver ions into the bladder. This dilutes the barrier effect and the desirability of continuous transfer of silver ions into the bladder is questionable. If the current applied throughout the catheter wall exceeds the sensory threshold an uncomfortable tingling sensation can also be felt.
The Ellis intraluminal electrode catheter with the silver anode attached on a wire lead ahead of the catheter and having the silver anode inserted directly into the bladder enhances the negative aspects of silver ion presence in the bladder. Silver ions produced in the urine can alter physiological conditions causing precipitation of salts and proteins. Also, an electrode inserted into and dwelling for an extended period in the bladder could become detached thus necessitating serious retrieval efforts and surgical procedures; likewise the wire lead ahead of the catheter could puncture tissue walls leading to serious complications. Further, the intraluminal route is not considered the major pathway for infection, which instead is believed to enter through the catheter/urethral wall interface. The catheter having the silver anode inserted directly into the bladder, has the additional drawback that little, if any, silver ion can reach the catheter/urethral wall interface and bactericidal action must take place within the bladder volume.